Crystal Growth of Al‐Rich Complex Metallic Phases in the System Al–Cr–Fe Using the Czochralski Method

Complex metallic phases in the Al-Cr-Fe system are considered to be interesting because of their enhanced resistance against corrosion. Single crystal growth of the Al(4)(Cr,Fe) and Al(13)(Fe,Cr)(4) phases, which is a prerequisite for detailed studies is presented herein for the first time. Along with their binary end members Al(4)Cr and Al(13)Fe(4) growth of cm(3)-size crystals was achieved by using the Czochralski method from Al-rich solutions at temperatures of approximately 1000 degrees C. Special emphasis is put on the refinement of the Al-rich corner of the ternary phase diagram in determining the 1000 degrees C equilibria between the incongruent melts and the corresponding ternary solid solutions. Our findings confirm earlier data on the existence region of Al(13)(Fe,Cr)(4), but significantly differ from those with respect to the so called Al(4)(Cr, Fe) phase. It is shown that the existence region of Al(4)(Cr,Fe) decomposes into four regions of structurally different phases depending on the Cr/Fe ratio. Binary mu-Al(4)Cr crystallizes in the hexagonal space group P6(3)/mmc and can dissolve only up to about 1 At-% iron. More Fe-rich alloys crystallize in the orthorhombic space group Cmcm (about 2 At-% iron) or Immm (containing between 3 and about 6 At-% iron). For crystals containing about 7 At-% iron the structure belongs to the space group R (3) over bar. The grown single crystals were characterized by electron probe microanalysis revealing only weak segregation effects. The structural perfection of the orthorhombic phase was studied using X-ray topography with the Lang technique. Significant anisotropic properties of this phase allow to discuss structural similarities with decagonal quasicrystals.